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J Electrodiagn Neuromuscul Dis > Volume 24(3); 2022 > Article
Lee, Min, Lee, Kim, and Hyun: Venous Thoracic Outlet Syndrome Combined with Brachial Neuritis Caused by Lymphadenopathy after Vaccination for Coronavirus Disease 2019: A Case Report


Thoracic outlet syndrome (TOS) occurs due to compression of the neurovascular bundle exiting the thoracic outlet, through which the brachial plexus and subclavian vessels pass. Here, we report a case of venous TOS combined with brachial neuritis, which was caused by axillary lymphadenopathy after the first dose of the BNT162b2 vaccine against coronavirus disease 2019 (COVID-19). A 17-year-old female patient presented with left upper extremity swelling and pain after inoculation with the BNT162b2 vaccine in the left deltoid muscle. Contrast-enhanced brachial plexus magnetic resonance imaging revealed severe swelling of the left axillary and subclavian lymph nodes, which lie immediately above the subclavian vein. An electrodiagnostic study revealed left brachial plexopathy, mainly involving the lower trunk with mixed demyelinating and axonal injury. The patient received intravenous steroid pulse therapy and oral steroid therapy. A follow-up examination showed complete recovery of muscle strength and function, pain, and swelling in the left upper extremity within 3 months after vaccination against COVID-19.


Thoracic outlet syndrome can occur from compression of the neurovascular bundle exiting the thoracic outlet, through which the brachial plexus and subclavian vessels locate. Entrapment of the axillary and subclavian vessels results in vascular TOS, which is subclassified into arterial and venous types [1]. Impingement of the brachial plexus results in neurogenic TOS. The reported incidence of TOS is 3-80 / 1000 (0.3-8%) and neurogenic TOS accounts for over 90% of all TOS cases [1].
There are a few case reports of acute brachial neuritis following coronavirus disease 2019 (COVID-19) vaccination [2,3]. Several reports have also documented reactive axillary lymphadenopathy as a common adverse effect of mRNA COVID-19 vaccines [4]. If lymphadenopathy is severe enough, subclavian and axillary vascular flow can be compromised, causing venous TOS [5]. No cases of combined venous TOS and brachial neuritis after COVID-19 vaccination have been reported to date. In this case report, we present the clinical manifestations and electromyographic characteristics of a patient diagnosed with both venous TOS and brachial neuritis after receiving an mRNA vaccine against COVID-19.

Case Report

A 17-year-old female presented with left upper extremity swelling and pain after inoculation with the BNT162b2 vaccine against coronavirus disease 2019 (COVID-19) in the left deltoid muscle. Pain and swelling in the upper arm started approximately 2 hours after the vaccination and spread to the lower arm and hand on the day after vaccination. However, she only observed this symptom and waited for it to subside, knowing that pain and swelling are very common side effects of mRNA vaccines. Although the swelling improved slowly, left arm weakness newly developed 2 weeks later. At that time, only hand swelling below the wrist was noticed, with a reticulated erythematous patch on the dorsum of the hand, implying problems with the peripheral circulation (Fig. 1). This study was approved by the ethics committee at the Seoul National University Hospital Institutional Review Board (2206-054-1331) and informed written consent was obtained from the patient.
She visited the Department of Pediatrics 2 weeks after the onset of left arm weakness. A neurological examination revealed motor weakness of grade 3 to 4 in the left upper extremity based on the Medical Research Council scale (left shoulder abductor grade 3-, elbow flexor grade 3-, elbow extensor grade 4, wrist dorsiflexor grade 3-, finger abductor grade 3, and finger flexor grade 3-). She reported hypesthesia in the entire left arm and paresthesia in the left palm. Adson’s test and Wright’s test were positive, while the costoclavicular test was negative. Laboratory investigations, including complete blood count, electrolytes, creatine kinase, and lactate dehydrogenase, were within normal ranges. The results of other autoimmune-related laboratory tests, such as anti-double-stranded DNA, fluorescent antinuclear antibody, lupus anticoagulant antibody, and antiphospholipid antibody, were also unremarkable. Contrast-enhanced left brachial plexus magnetic resonance imaging (MRI) was performed 3 weeks after the onset of left arm weakness. Brachial plexus MRI revealed bilateral—yet left upper extremity predominant—lymphadenopathy, including severe swelling of the left axillary nodes and subclavian lymph nodes, which lie immediately above the subclavian vein (Fig. 2).
A nerve conduction study (NCS) was performed 3 weeks after the onset of weakness to diagnose possible immune-mediated polyneuropathy at the Department of Rehabilitation Medicine. The latency and amplitude of the sensory nerve action potentials (SNAPs) of the bilateral median, ulnar, radial, lateral antecubital cutaneous, and medial antebrachial cutaneous nerves were symmetric (Table 1). No prolongation of the F-wave or the H-reflex was observed.
Needle electromyography (EMG) revealed prominent denervation potentials and neuropathic motor unit action potentials (MUAPs) in the left extensor indicis, abductor pollicis brevis, and first dorsal interosseous muscles from the lower trunk (Table 2, Fig. 3). The left biceps and deltoid muscles exhibited short duration and polyphasic MUAPs, indicating nascent motor units with relatively less abnormal spontaneous activity than muscles from the lower trunk. These neuropathic MUAPs with denervation potentials indicated axonal injuries in the left brachial plexus. Compared to the symmetric CMAP amplitudes, however, the denervation potentials were extremely prominent, and the interference patterns of MUAPs were reduced, especially in the muscles from the lower trunk, suggesting that proximal demyelination lesions were also present in addition to axonal injuries. Therefore, the electrodiagnostic study concluded that the patient had left brachial plexopathy, mainly involving the lower trunk, with mixed demyelination and axonal involvement.
After intravenous steroid pulse therapy for 3 days and maintenance for 4 months, a follow-up examination showed complete recovery of muscle strength in the left upper extremity, pain, and swelling within 3 months after the vaccination.


The clinical course of brachial neuritis consists of sudden, severe neuropathic pain, fast multifocal weakness, and atrophy of the upper extremities [6], preceded by infection, trauma, or inflammation, including COVID-19 vaccination [2,6]. This patient first presented with left arm swelling and pain after the first dose of the BNT162b2 vaccine, followed by left arm weakness, which is a typical characteristic of brachial neuritis after vaccination. Interestingly, neurogenic motor and sensory symptoms, as well as lymphadenopathy, have been reported to occur more frequently on the same side of the vaccine injection [2,4]. Although there is no proven effective treatment of brachial neuritis, a retrospective study showed that corticosteroid administration in the acute phase shortened pain and accelerated recovery [7]. This patient was also treated with a corticosteroid to reduce pain and promote recovery.
An electrodiagnostic study is one of the examinations for confirming brachial neuritis. Although sensory nerve conduction studies are useful for diagnosing peripheral neuropathies or brachial plexopathies, the sensory NCS is reported to be normal in 80% of patients with brachial neuritis [8]. Although the motor NCS can reveal axonal loss, needle EMG is more sensitive for detecting signs of denervation or reinnervation when clinically affected muscles are examined [9]. In this case, the patient showed nearly symmetric SNAP and CMAP amplitudes, and needle EMG showed an axonal neuropathic injury, which is comparable to brachial neuritis. Denervation potentials, observed at the muscles innervated from lower trunk, could be seen not only in axonal injuries but also in pure peripheral demyelinating neuropathy [10]. This electrodiagnostic study suggested axonal injuries were present, but not very severe depending on NCS result, and both EMG and the patient’s inconsistent weakness compared to CMAP supported a presence of combined demyelinating lesions.
The diagnosis of venous TOS requires a comprehensive consideration of the patient’s history, a physical examination, and imaging techniques [1]. Venous TOS is characterized by the pathognomonic presentation of acute upper extremity swelling, cyanosis, heaviness, and ultimately pain [1]. This patient also presented with not only acute left upper extremity pain, but also extreme swelling of the entire arm and signs of vascular compromise. She exhibited positive signs on Adson’s and Wright’s tests, which are provoked by an exaggerated blockage of vascular flow. Brachial plexus MRI confirmed prominent but asymmetric axillary lymphadenopathy, and the swollen left subclavicular lymph node was located at the thoracic outlet (Fig. 2). Several previous studies have reported a correlation between axillary lymphadenopathy and COVID-19 vaccination [4]. Patients receiving the BNT162b2 vaccine demonstrated higher rates of palpable unilateral axillary lymphadenopathy than those receiving placebo [11]. Enlarged subclavian lymph nodes, as in this case, could impede flow through the subclavian vein within the costoclavicular space, resulting in venous TOS.
Although brachial neuritis is usually self-limiting, the previously reported recovery rate is 36% by 1 year, 75% by 2 years, and 89% by 3 years [12], and no prognostic factors are yet known [2]. This case showed relatively early and complete recovery within 3 months after vaccination. As the degree of axonal loss is correlated with CMAP or SNAP and determines the permanent impairment of neuropathy, normal NCS from this case can explain the early recovery [6]. In addition, most cases of reactive ipsilateral axillary lymphadenopathy after COVID-19 vaccination recovered within 10 weeks after vaccination [13]. With the rapid resolution of lymphadenopathy and disrupted venous flow, the clinical symptoms caused by venous TOS could improve within months, which might have also contributed to the patient’s early recovery. Since the clinical course could be different among patients, previously reported cases of brachial neuritis after vaccination should also include information about both the amount of axonal loss and any vascular compromise to reveal the possibility of concomitant venous TOS caused by lymphadenopathy. Any supportive evidence of combined venous TOS—more specifically, vascular symptoms, such as swelling, cyanosis, erythematous skin change, and vascular compression provocation tests— should be evaluated to clarify whether brachial neurities with concomitant venous TOS has a different prognosis from brachial neuritis alone.
In conclusion, brachial neuritis combined with an interruption of subclavian vessels and venous TOS followed by lymphadenopathy can occur after COVID-19 vaccination. Therefore, clinicians should evaluate vascular symptoms and neurological examinations to consider the possibility of combined venous TOS before confirming post-vaccine brachial neuritis if sudden weakness with dominant swelling and erythema occurs after a vaccination. Although follow-up electrodiagnostic studies and MRI were not conducted in this study, which would have provided more accurate evidence of the patient’s full recovery, this case report suggests the possibility of different pathomechanisms corresponding to diverse prognoses and recovery potentials of brachial neuritis after vaccination.

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Fig. 1.
A reticulated erythematous patch (arrows) and swelling on the dorsum of the left hand 1 month after a vaccine inoculation that was administered in the ipsilateral, left deltoid muscle.
Fig. 2.
(A) Coronal view of brachial plexus magnetic resonance imaging (MRI) demonstrating an enlarged subclavian lymph node (straight arrow) compressing the subclavian vein (white arrowhead). An enlarged lymph node (curved arrow) near the left brachial plexus (empty arrowhead) is also apparent, but not compressing the brachial plexus. (B) Transverse view of brachial plexus MRI imaging demonstrating the relationship of the subclavian vein (white arrowhead) with the enlarged subclavian lymph node (straight arrow) and the brachial plexus (empty arrowhead).
Fig. 3.
(A) Abnormal spontaneous activities in the left first dorsal interosseous muscle. (B) Abnormal spontaneous activities in the left abductor pollicis brevis muscle. EMG, electromyography.
Table 1.
Nerve Conduction Study Results
Nerve (recording) Stimulation Latency (ms)
Duration (ms)
Area (mV·ms )
Conduction velocity (m/s)
Right Left Right Left Right Left Right Left Right Left
Motor NCS
 Median (APB) Wrist 3.07 3.54 9.9 9.6 21.3 20.16 52.2 60.6
Elbow 6.67 7.14 9.9 9.7 21.25 20.99 50.1 56.5 55.7 61.2
Erb’s point 11.93 9.3 - 21.82 - 52.6 - 71.0
 Ulnar (ADM) Wrist 3.03 2.55 5.6 5.9 25.99 28.91 28.30 55.3
Below elbow 5.89 5.52 5.4 5.9 26.2 28.91 26.90 47.4 67.8 64.0
Above elbow 7.5 7.14 5.3 5.8 26.3 29.90 27.40 53.3 61.9 61.9
 Axillary (deltoid) Erb’s point 3.07 3.02 16.9 14.8 26.2 31.65 182.80 189.80
 Suprascapular (SST) Erb’s point 1.82 2.50 10.8 9.4 26.25 24.79 130.90 117.50
 Musculocutaneous (biceps) Erb’s point 3.96 3.39 14.3 10.5 34.43 38.28 143.80 112.90
 Radial (EIP) Forearm 2.45 2.76 5.1 3.8 - - - -
Elbow 5.47 5.99 4.0 3.1 - - - - 59.6 55.7
 Median (APB) Wrist 22.50 22.66
 Ulnar (ADM) Wrist 24.32 23.44
Sensory NCS
 Median (digit II) Wrist 2.29 2.29 42.4 43.1
 Ulnar (digit V) Wrist 2.29 2.66 25.5 26.9
 Radial (snuff box) Forearm 1.88 1.72 37.5 33.5
 LAC (forearm) Forearm 1.20 1.41 26.7 29.2
 MAC (forearm) Forearm 1.56 1.35 14.9 13.5

Amplitudes are measured in millivolt (mV, motor) and microvolt (μV, sensory).

NCS, nerve conduction study; APB, abductor pollicis brevis; ADM, abductor digiti minimi; SST, supraspinatus; EIP, extensor indicis proprius; LAC, lateral antebrachial cutaneous; MAC, medial antebrachial cutaneous.

Table 2.
Needle Electromyography Results
Muscle IA Spontaneous
Recruitment pattern/IP
Fib/PSW Other Amplitude Duration Polyphasicity
Lt. extensor indicis Increased 3+/3+ None N N N Discrete
Lt. abductor pollicis brevis N 4+/4+ None No activity
Lt. first dorsal interosseous N 4+/4+ None N N Increased Discrete
Lt. biceps brachii N 2+/2+ None N Short Increased Reduced
Lt. deltoid N 1+/1+ None N Short N Reduced/complete
Lt. abductor hallucis Increased 0/0 CRD (1+) N N N Complete
Lt. vastus medialis N 0/0 None N N N Discrete
Rt. extensor indicis Increased 0/0 None N N N Reduced/complete

IA, insertional activity; Fib, fibrillation; PSW, positive sharp wave; MUAP, motor unit action potential; IP, interference pattern; Lt., left; Rt., right; N, normal; CRD, complex repetitive discharge.


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